Review devman repo and add test automation

[Bullish-Design]

This commit addresses multiple critical and major issues found during code review, adds a comprehensive test suite, and sets up CI/CD.

CRITICAL FIXES:

• Fix import error in commands/init.py (missing index module functions)
• Add missing run() function to switch.py command
• Update version to 0.2.0 across all files for consistency
• Remove unused jinja2 dependency from flake.nix
• Fix potential None dereference in up.py _load_nvim_session

MAJOR FIXES:

• Replace ValueError with typer.Exit in commands for better UX
• Add missing bootstrap command registration in CLI
• Fix subprocess resource leak in nvim integration
• Standardize type annotations (remove old-style Dict, Optional)
• Add encoding="utf-8" to all file I/O operations

TEST SUITE:

• Add comprehensive unit tests for discovery module (13 tests)
• Add comprehensive unit tests for state module (6 tests)
• Add comprehensive unit tests for loaders module (7 tests)
• Add comprehensive unit tests for commands module (11 tests)
• Add comprehensive unit tests for integrations module (15 tests)
• Add comprehensive unit tests for onboarding module (9 tests)
• Add comprehensive unit tests for models module (11 tests)
• Total: 72 new tests covering previously untested modules

CI/CD:

• Add GitHub Actions workflow for automated testing
• Configure pytest with coverage reporting
• Add PR comment action to post test results and coverage
• Support Python 3.11, 3.12, and 3.13
• Add Nix build verification
• Set coverage threshold to 70%

COVERAGE IMPROVEMENTS:

• Before: ~15% coverage (only 3 test files, 11 tests)
• After: Expected 70%+ coverage (10 test files, 83+ tests)

This significantly improves code quality, reliability, and maintainability.